Field of the Invention
The invention relates to a device for processing substrates. The device has a first laser source for generating a first laser beam, a first beam expander in the beam path of the first laser beam, a deflecting unit, and an optical imaging device. These are arranged in series in the beam path of the first laser beam and image the first laser beam on the substrate. The invention further pertains to a method in which such a device is used in the processing of substrates.
As a rule, use is made of standard lasers such as Nd:YAG, Nd:YVO4, CO2, argon ion or other lasers known per se when processing substrates by means of laser beams, for example when structuring metalized substrate surfaces or when boring contact holes in multilayer substrates. The output beams of these lasers are imaged on the substrate to be processed by a beam expander, a deflecting unit and an optical imaging device, mostly an f-theta lens with a focal length of between 150 mm and 50 mm.
In order to achieve as large an energy density as possible and a high resolution when processing the substrate, the energy of the laser is focused in this case on as small an area as possible, the so-called minimum spot size, which is be found in the focal plane of the optical imaging device on account of the laser beam incident on the optical imaging device from the beam expander as a parallel beam. Upstream and downstream of the focal plane, the spot size of the laser is larger, and therefore only a smaller energy density is achieved there. The spacing between the positions upstream and downstream of the focal plane of the two spot sizes which are regarded as just adequate for the processing, is denoted below as depth of focus. The depth of focus is yielded in a known way as a function of the wavelength of the laser light, the beam expansion and the focal length of the f-theta lens. In most applications, the depth of focus varies between 1 and 5 mm in the case of a wavelength of 1064 nm, and between 0.1 and 1 mm in the case of a wavelength of 266 nm.
When boring substrates with a thickness of the order of magnitude of the depth of focus, the problem now arises that because of the widening of the spot size at the border of the range of depth of focus, the hole is not characteristically cylindrical, but strongly conical. It is impossible to set the conicity of the hole because it is prescribed by the laser system used.
Various methods are known for changing the useful range of depth of focus. First, it would be possible to use a longer wavelength, but in this casexe2x80x94depending on the material of the substratexe2x80x94thermal effects occur which are partially destructive and therefore undesireable. Another possibility consists in a smaller beam expansion upstream of the optical imaging device, which leads to a larger depth of focus but also to a larger spot size which is not fine enough in the case of the finest structures and/or holes. Third, the displacement of the substrate in the direction of the laser beam during the structuring and/or boring operation remains, in order thus to remain in the range of the depth of focus. However, the mechanical arrangements required for this are too slow to reach as large a throughput as possible (for example more than 100 bored holes per second).
It is accordingly an object of the invention to provide a method and device for processing substrates, which overcomes the above-mentioned disadvantages of the heretofore-known devices and methods of this general type and which specifies a flexible, low-cost device for boring different substrates, and an associated method for using such the device.
With the foregoing and other objects in view there is provided, in accordance with the invention, a device for processing substrates, comprising:
a first laser source for generating a first laser beam projecting along a first beam path;
a first beam expander disposed in the first beam path;
a deflecting unit and an optical imaging device disposed in series in the first beam path for imaging the first laser beam onto a substrate;
a second laser source for generating a second laser beam projecting along a second beam path;
a second beam expander disposed in the second beam path;
a deflecting assembly disposed in the second beam path and configured to deflect the second laser beam to the deflecting unit and to be imaged on the substrate via the deflecting unit and the optical imaging device; and
wherein the first and second beam expanders are constructed such that, after the first and second laser beams are focussed by the optical imaging device, there exists a difference between minimum spot sizes of the first and second laser beams.
The expression xe2x80x9cdifferencexe2x80x9d with reference to the spot sizes means a difference in the position of the minimum spot sizes along a beam direction and/or a difference in the dimensions of the minimum spot sizes of the first and second laser beams.
The solution according to the invention ensures at least two different ranges of depth of focus which are used for processing different substrates.
In accordance with an added feature of the invention, the two laser sources are of identical design, as a result of which the two laser beams have the same wavelength, and the deflecting unit and the optical imaging device are to be designed only to this common wavelength.
In accordance with an additional feature of the invention, the second beam expander has a different magnification than the first beam expander, causing the minimum spot sizes of the first and second laser beams to differ. The different magnification of the beam expanders leads to two different ranges of depth of focus which can be used, for example, to achieve holes of different conicity.
In accordance with another feature of the invention, the second beam expander is maladjusted, as a result of which the position of the minimum spot of the second laser beam is displaced by comparison with the first laser beam. It is therefore possible to bore thin holes through thick substrates, since the divergence of the beam outside the range of depth of focus plays no role.
In accordance with a further feature of the invention, the second beam expander is variably maladjustable, such that the position of the minimum spot of the second laser beam is variably adjustable. By means of the variable maladjustment of the second beam expander the device can advantageously be adapted to substrates of different thickness.
In accordance with a preferred embodiment, the deflecting assembly comprises a deflection mirror and a semi-reflecting mirror.
With the above and other objects in view there is also provided, in accordance with the invention, a method of processing a substrate with the above-outlined device. The method comprises the following steps:
placing the device relative to a substrate and adjusting the positions of the minimum spot sizes to be located at different depths in the substrate;
boring a first hole in the substrate with the first laser beam substantially to the position of the minimum spot size of the first laser beam; and
boring the hole further with the second laser beam.
In accordance with again an added feature of the invention, lasers are used with laser beams having mutually different wavelengths. The laser beams are preferably pulsed laser beams. By using different wavelengths it is possible, above all, to process multilayer substrates with wavelengths adapted to the respective layers.
In accordance with a concomitant feature of the invention, the laser beams are pulsed with mutually different pulse energies and/or mutually different pulse repetition rates. This feature adds further flexibility in the process.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a device for processing substrates, and method using such a device, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.